Nonmagnetic corrosion-resistant drill string members

ABSTRACT

A drill string for deep-well drilling, coring and the like is composed of lengths unitarily formed of a nonmagnetic, highnitrogen, chromium-nickel austenitic alloy steel and has a pair of threaded ends matingly engageable with the complementary ends of adjoining lengths and an intermediate or central portion between these ends. The drill-string members are composed of alloy steel containing from trace amounts to 0.07 per cent by weight carbon, trace amounts to 1.00 per cent by weight silicon, 0.50 to 2.00 per cent by weight manganese, 20.0 to 25.0 per cent by weight chromium, 10.0 to 15.0 per cent by weight nickel, 0.05 to 0.50 per cent by weight nitrogen and the balance iron and the usual impurities present in chromium-nickel alloy steels. The drill-string members are resistant to stress corrosion cracking and have their central zones worked (hot/cold working) to a yield point up to 70 kp/mm2 (0.2 percent elongation) while the threaded end portions are hot/cold worked to a yield point above the minimum of (0.2 percent elongation) 70 kp/mm2.

United States Patent 1151 3,659,882 Souresny [4 1 I May 2, 1972 s41 NONMAGNETIC CORROSION- 3,112,195 11/1963 Souresny ..75/l26R RESISTANT DRILL STRING MEMBERS Primary ExaminerDave W. Arola [72] Inventor: Herbert Souresny, Ternitz, Austria Anomey Kafl E Ross 73 Assi nee: Schoeller-Bleckman Stahlwerke Aktlen- 1 g gesellschaft, Vienna, Austria ABSTRACT [22] Filed, 1, 1969 A drill string for deep-well drilling, coring and the like is composed of lengths unitarily formed of a nonmagnetic, high- [21] Appl. No.: 881,154 nitrogen, chromium-nickel austenitic alloy steel and has a pair of threaded ends matingly engageable with the complementar ends of ad'oinin len ths and an intermediate or central [30] Forelgn Appucauon Priority Data pzmion betwe en th ese finds. The drill-string members are Dec. 2, 1968 Austria ..A1 1685/68 Composed of alloy Steel containing from trace amounts to per cent by weight carbon, trace amounts to 1.00 per cent by 52 U.S. c1 ..285/333,75/128,148/37, weight silicon, 050 w P cent y weight manganese, 22 20.0 to 25.0 per cent by weight chromium, 10.0 to 15.0 per 51 Int. Cl ..F16l 25 00 cent by Weight nickel, to P cent by weight nitrogen [58] Field of Search ..75/l26 R, 128 R, 128 A, 128 N; and the balame iron and the usual impurities Present in 148/4 37; 285/333 334 422; 287/125 chromium-nickel alloy steels. The drill-string members are re sistant to stress corrosion cracking and have their central zones worked (hot/cold working) to a yield point up to 70 [56] Relerences Cited kp/mm' (0.2 percent elongation) while the threaded end por- UNITED STATES PATENTS tions are hot/cold worked to a yield point above the minimum of (0.2 percent elongation) 70 kp/mm. 2,121,391 6/1938 Amess ..75/128 N 2,676,820 4/1954 Boice ..285/333 X 2 Claims, 1 Drawing Figure Up to 0.07% 0 Up to 1.00% Si 0.50 to 2.00% Mn 20.0 to 25.00% Cr no '0 '50 Ni Threaded and yield point '3 H '6 l5 05 to 5% N TOkp/rnm (0.2% elongation Bol. Fm! imp.

hot/cold workin Hot/cold working to control 2l 20 zone yield p int -7'0lt1 II Nonmoqnetic stress-corroslon-reslstunt (02% alonqatron) drill-string length NONMAGNETIC CORROSION-RESISTANT DRILL STRING MEMBERS FIELD OF THE INVENTION and better nonmagnetic character than has been obtainable heretofore.

BACKGROUND OF THE INVENTION The stringent requirements of deep drilling (i.e., drilling for subsurface deposits of gas and petroleum, deep-well drilling for mineral and water recovery, coring for subsurface and strata analysis and the like) generally makes use of a drill string consisting of interconnected lengths or members, the ends of which are threaded for engagement with the complementary ends of the adjoining lengths.

Frequently the string must be used to guide a magnetometer or other magnetically responsive instrument to subsurface levels for geological exploration, investigation of the geological formations, analysis of the progress of drilling or the like. To this end it is important that the drill string be more or less nonmagnetic or nonmagnetizable and it has of course been proposed heretofore to provide nonmagnetic or nonmagnetizable drill strings whose central bore could accommodate a measuring instrument of this nature without adversely affecting the readings thereof.

In one prior-art system, the drill string is composed of a metal alloy predominantly consisting of nickel, especially an alloy of 65 percent by weight nickel, 25 percent by weight copper and a maximum of 5 percent by weight aluminum. Drill-string lengths or parts composed of this alloy were nonmagnetic and possessed, for the most part, mechanical strength properties recognized as desirable in drill-string members. A disadvantage of such a system is the high cost of the alloy and the drill string and thus it has long been desired to provide less expensive and still further improved alloys for use in drill strings, and to provide drill strings of improved properties.

It has, for example, been proposed to provide drill strings from conventional l8/8 chromium-nickel stainless steel having an austenitic crystallographic, microcrystalline, grain or lattice structure. In practice, however, drill strings composed of such alloys have generally been unsatisfactory both with respect to the requirement that the drill string be nonmagnetic and with respect to the insufficient strength of the steel which has a yield point well below the minimum permissable for use in deep-drilling systems.

Moreover, the drill-string members of this composition fail to withstand the corrosive action within the bore and create difficulties in this regard as well. To avoid these disadvantages, it has been suggested to substitute magnetic or magnetizable portions or collars of higher quality steel, less susceptible to corrosion, at the threaded ends of the drill-string length. These end portions are welded to the central or body portion which is composed of the nonmagnetic or nonmagnetizable alloy. While corrosion affects such composite drill-string members to a lesser extent, a further disadvantage is created because the magnetic portions of the member impede or disrupt operation of the measuring device.

OBJECTS OF THE INVENTION It is, therefore, the principal object of the present invention to provide an improved drill string or drill-string member which will obviate the above-mentioned disadvantages and constitute a significant advance over earlier drill strings.

SUMMARY OF THE INVENTION This object and others which will become apparent hereinafter is attained with a drill-string member having a pair of threaded end portions unitarily and monolithically integral with a central zone or body and composed of one piece; the member is fonned of a steel alloy with an austenitic and nonmagnetic character and which nevertheless is stress-corrosioncracking resistant.

The composition or alloy, according to this invention, consists of up to (from trace amounts) 0.07 percent by weight carbon, up to (from trace amounts) 1.00 percent by weight silicon, 050 to 2.00 percent by weight manganese, 20.00 to 25.00 per cent by weight chromium, 10.00 to 15.00 per cent by weight nickel and 0.05 to 0.50 per cent by weight nitrogen, the balance iron and the usual impurities associated with chromium-nickel steel alloys and which do not affect the properties thereof.

It is essential for the purposes of the present invention that the central zone of the drill-string length (between the coupling ends), be subjected to so-called hot/cold working at a temperature of 500 to 800 C. to a yield point up to 70 kp/mm (kiloponds per millimeter square) at 0.2 percent elongation, while the ends or threaded portions of the drill string member are hot/cold worked at this temperature to a minimum yield point (0.2 percent elongation) of 70 kp/mm'- The resulting body has a surprising resistance to stress-corrosion cracking and is capable of withstanding the mechanical rigors of deep drilling while being as nonmagnetizable as the best nonmagnetic materials heretofore used in drill strings. I am aware that it has been proposed heretofore to make use of manganese austenite to overcome some of the disadvantages of earlier compositions and even to add chromium to form manganese chromium alloys for drill strings. Hot/cold forming and working has been proposed in conjunction with these latter compositions which, however, are susceptible to severe attack by the corrosive chloride solutions frequently encountered in drilling.

Stresscorrosion cracking is particularly severe on compositions of the latter type so that it is altogether surprising that chromium-nickel austenitic steels of the invention with the relatively high manganese content of 0.5 to 2.00 per cent by weight has a significant resistance to stress-corrosion cracking. In fact, tests of drill-string members, in accordance with the present invention, show that even with strong deformation under stresses of the order of the yield point and in the presence of boiling synthetic sea water as a corrosive enveronment, the members resist stress-corrosion cracking for periods of 5,000 hours or more.

DESCRIPTION OF THE. DRAWING The above and other objects, features and advantages of this invention will become more readily apparent from the following description, reference being made to the accompanying drawing and the following specific example. The sole FIGURE of the drawing represents an elevational view of a drill string, partly broken away.

SPECIFIC DESCRIPTION In the drawing I show a drill string constituted of a plurality of axially interconnected drill-string lengths 10 and 20 each of which has a central portion or zone 15 of generally cylindrical configuration and provided with a central bore 16 through which a magnetically responsive measuring device may be passed.

At one end, each length is provided with a threaded end portion 11 with a female thread 13 adapted to receive the male thread 14 at the other threaded end 12 of an adjoining drill-string length. The female threaded end 21 is shown to receive the male threaded end 14 at the coupling of the members l0 and 20.

As noted in the drawing, the drill-string members 10 and 20 are composed of nonmagnetic stress-corrosion cracking highresistant austenitic steel consisting up to 0.07 percent of carbon, up to 1.00 percent of silicon, 0.5 to 2.00 percent of manganese, 20 to 25 percent of chromium, l0 to 15 percent of Balance lron and trace impurities which do not affect the properties of the alloy.

The tests detailed below were found to yield similar results, within the range of experimental error, when the silicon content was varied between 1.00 and 1.10 percent by weight, the chromium content was varied between 21.50 and 23.00 percent by weight, the nickel content was varied between 12.00 and 13.0 percent by weight and the nitrogen content was varied between 0.27 and 0.32 percent by weight.

The aforementioned composition was machined to produce drill-string lengths of the type described in my prior U.S. Pat. No. 3,112,195 issued Nov. 26 1963.

For the central portion of the members, the following physical properties were found (after hot/cold working at a temperature of about 750 C.

Yield Point (0.2% Elongation) 58.6 kp/mnt square centimeter) In two tests the threaded ends were found to have the following characteristics:

Test 1 Test ll Yield Point (0.2% Elongation) 87.7 lip/mm 84.0 kp/mm' Tensile Strength 95.2 lip/mm 92.4 kp/mm' Elongation l- M) 28.0% 27.0% Reduction in Area (Contraction) 64.0% 65.0% Notched-bar lmpact-strength 15.0 mkp/cm 15.6 mkp/cm (Chal'PY The permeability of the drill-string member had a value less than 1.005 Gauss/Oersted with a field intensity of l00/Oersted. Tests in boiling synthetic sea water, after stressing the member substantially to the value of its yield point at the central and end zones, shows no stress-corrosion cracking after 5,000 hours. The drill-string members can be made to a length of 10 meters without difiiculty and are highly effective in chloride environments and in deep-well drilling in general.

What is claimed is:

1. A drill-string length having a central body portion and a pair of complementarily threaded end portions, said portions being formed in one piece from a nonmagnetizable austenitic nickel-chromium steel alloy resistant to stress-corrosion cracking and consisting essentially of trace amounts to 0.07 percent by weight carbon, trace amounts to 1.00 percent by wci t silicon 0.50 to 2.00 rcent b wei t man ese 20. 0 to 25.00 percent by weight chrori tium, l 0.00 to 1 5.

percent by weight nickel, and 0.05 to 0.50 percent by weight nitrogen, the balance being iron and the usual impurities, said central portion being hot/cold worked to a yield point up to 70 ltp/mm (0.2 percent elongation) and said end portions being hot/cold worked to a yield point of at least 70 lip/mm (0.2 percent elongation).

2. The drill-string length defined in claim 1 wherein said alloy has the following composition:

Up to 0.05% Carbon 0.35 to 0.60% Silicon 1.00 to 1.10% Manganese 2 L50 to 23.00% Chromium 12.00 to 13.00% Nickel 0.27 to 0.32% Nitrogen Balance lron and Impurities 

1. A drill-string length having a central body portion and a pair of complementarily threaded end portions, said portions being formed in one piece from a nonmagnetizable austenitic nickel-chromium steel alloy resistant to stress-corrosion cracking and consisting essentially of trace amounts to 0.07 percent by weight carbon, trace amounts to 1.00 percent by weight silicon, 0.50 to 2.00 percent by weight manganese, 20.00 to 25.00 percent by weight chromium, 10.00 to 15.00 percent by weight nickel, and 0.05 to 0.50 percent by weight nitrogen, the balance being iron and the usual impurities, said central portion being hot/cold worked to a yield point up to 70 kp/mm2 (0.2 percent elongation) and said end portions being hot/cold worked to a yield point of at least 70 kp/mm2 (0.2 percent elongation).
 2. The drill-string length defined in claim 1 wherein said alloy has the following composition: Up to 0.05% Carbon 0.35 to 0.60% Silicon 1.00 to 1.10% Manganese 21.50 to 23.00% Chromium 12.00 to 13.00% Nickel 0.27 to 0.32% Nitrogen Balance Iron and Impurities 